1. Field of the Invention
The present invention relates to a protective device for detecting an abnormal condition or faults for the rotor of a brushless exciting device. Some of these faults are: a fault in an arm of a rectifying circuit; and the faulty grounding of an armature winding of an AC exciting device.
2. Description of the Prior Art
Heretofore, various devices have been proposed as devices for detecting an abnormal fault in a rotor of a brushless exciting device.
For example, it has been proposed to detect the fault in an arm of the rectifying circuit by a detecting winding disposed on a field pole of the AC exciting device. It has also been proposed to detect a faulty ground by measuring an insulation resistance after applying a voltage between the ground and a desired position of the electric circuit of the rotor through a slip ring.
However, a separate detecting circuit, a separate signal circuit and a separate power source circuit are required to detect all of the abnormal faults in such abnormal fault detecting device. The wirings are complicated in such a protective device and this can easily cause erroneous connection or erroneous operation and be expensive.
The kinds of faults detected by these devices are limited and sometimes, certain faults of the rotor can not be detected.